1. Field of the Invention
The invention relates to the field of apparatus and processes for the manufacture of composite parts or structures and, in particular, to the field of apparatus and processes for the manufacture of composite parts wherein resin is injected into a lay-up of fibrous materials positioned in a mold.
2. Description of Related Art
A typical method of manufacturing composite pads involves the steps of laying up structural filamentary material pre-impregnated with a resin in a mold, vacuum bagging the lay-up, drawing a vacuum from between the bag and mold such that the lay-up is compressed by atmospheric pressure against the mold while, and, finally, heating the resin impregnated filamentary material until the resin is cured. However, pre-impregnated filamentary material is expensive, its shelf life is limited, and it must normally be kept refrigerated until used. Additionally, the number of resin/filamentary material combinations is limited. Furthermore, special handling safety procedures are necessary when handling uncured resin impregnated materials.
This has led to the use of processes that do not require such "prepregs", as they are often called. These processes are similar in that structural filamentary material is still laid up in a mold, however it is resin free, the lay up is vacuum bagged, a vacuum is drawn from between the bag and mold such that the lay-up is compressed by atmospheric against the mold. However, in this process, resin is simultaneously drawn in through an inlet port in the vacuum bag and through the lay-up impregnating it. Finally, the now impregnated filamentary material is heated until the resin is cured. Such a process is essentially disclosed in British Patent No. 944,955 "Improvements In Or Relating To Methods Of Producing Reinforced Plastic Structures" by P. R. Green. Another approach is found in U.S. Pat. No. 2,913,036 "Process And Apparatus For Molding Large Plastic Structures" by G. H. Smith. Here the lay-up is placed over a mold. The lay-up itself incorporates a plurality of channels wherein resin can flow from the periphery of the lay-up upward to the center thereof. Thus after vacuum bagging, the resin is pumped into the lay-up from the periphery of the mold while a vacuum is pulled from a plurality of locations in the center.
This resin distribution problem was also addressed in U.S. Pat. No. 4,132,755 "Process For Manufacturing Resin Impregnated Reinforced Articles Without The Presence of Resin Fumes" by J. Johnson. This process includes the steps of placing the lay-up in a mold; placing a sheet of flexible material containing a plurality of dispersed perforations thereover and sealing its periphery to the mold so as to define a sealed inner chamber in which the lay-up is contained; placing a sheet of impervious flexible material (vacuum bag) over the sheet of perforated flexible material, with the periphery thereof also sealed to the mold so as to define a sealed outer chamber in which the inner chamber is contained, connecting the inner chamber to a vacuum source so as to draw the vacuum bag and perforated sheet, against the lay-up; and connecting the outer chamber to a source of resin so that the resin is passed from the outer chamber into the reinforcing material through the perforations of the first-mentioned sheet and into the lay-up.
Japanese patent no. 60-83826 contemplates the use of a woven plastic resin flow layer (No. 10 mesh) with a thickness of 1.05 mm to distribute the resin into the lay-up. In U.S. Pat. No. 4,902,215 "Plastic Transfer Molding Techniques For the Production of Fiber Reinforced Plastic Structures" By W. H. Seemann the apparatus includes a mold over which a fluid impervious outer sheet or vacuum bag, having a resin inlet port, that is marginally sealed to the mold forming a chamber in which the lay-up is placed for subsequent molding. A vacuum outlet port is provided for drawing a vacuum from the chamber. A resin distribution medium is positioned between the lay-up and vacuum bag. In one embodiment, the distribution medium is a sheet comprising an open network of non-swelling, non-resin absorbing intersecting monofilaments having pillar like members at the intersections. In a second embodiment, the distribution medium includes intersecting strips. In a third embodiment the distribution medium is a weaved or knitted plastic fabric. In addition, a distribution means or channel formed by incorporating a helical spring between the lay-up and vacuum bag extending from the resin inlet across the distribution medium, insures that the resin is evenly distributed. A vacuum is drawn via the outlet port and resin is drawn in through the inlet port. Drawing of the vacuum causes the vacuum bag to collapse down on the lay-up and form the lay-up against the mold. However, the resin distribution medium insures that the resin is distributed evenly over the lay-up by keeping the vacuum bag from collapsing onto the lay-up.
The inventor claims that due to its open pillar-like structure of the distribution medium and the continuous network of lateral openings lying between these pillars, a continuous network of passageways in all direction is provided from the point of entry of the resin, or fluid plastic, over the whole area of the distribution medium. In applicant's co-pending U.S. patent application Ser. No. 417,521 "Apparatus for Fabricating Composite Parts", filed Jun. 6, 1995 the use of resin distribution mediums made of woven or knitted wire mesh in an apparatus for forming such composite structures. The use of the high modulus materials prevents local collapse thereof and also acts as a caul plate further eliminating the possibility of resin starved areas.
All of these patents except those to Seemann did not address the need to insure that the "vacuum path" remains open so that it is equally drawn from all areas of the lay-up. Seemann's approach is to install a spiral spring between the lay-up and outlet port so that the vacuum bag can not collapse about the inlet to the port. However, such a spiral spring does little to insure that the vacuum is drawn evenly from the entire lay-up.
Thus it is a primary object of the subject invention to provide an apparatus and process for making composite parts.
It is another primary object of the subject invention to provide an apparatus and process for making composite parts using non-impregnated filamentary material..
It is a further object of the subject invention to provide an apparatus and process for making composite parts using non-impregnated filamentary material that includes a resin distribution medium that insures even resin distribution throughout the lay-up and, a distribution medium positioned over the lay-up to insure that a vacuum is drawn equally from all parts of the lay-up.